The present invention relates generally to gas turbine engines, and more particularly to a heat transfer fin configuration formed in a conduit of a coaxial heat exchanger, and a method of creating the same.
Both plate and cylindrical heat exchangers are well known and used in various applications, including gas turbine engines. The heat transfer performance advantages possible with plate heat exchangers are also well known, often resulting from a greater fin configuration flexibility and the ability to manufacture a flat plate with more densely packed fins than is generally possible with cylindrical type heat exchangers. However, in order to provide sufficient heat transfer, plate-fin type heat exchangers must be relatively large. In comparison, cylindrical heat exchangers are significantly more compact, and can offer considerable weight and part number reductions relative to flat plate heat exchangers. However, cylindrical heat exchangers often fail to provide performance equivalent to that of a corresponding plate heat exchanger.
Cylindrical heat exchangers are generally composed of at least two concentric pipes, each providing a path for a fluid to flow therethrough, such that a hotter fluid flowing through the first pipe can transfer heat to a cooler fluid flowing through the second pipe. To improve heat transfer, it is known to have fins, often longitudinally extending, projecting into both pipes from a common wall. Such an inner tube 10 of cylindrical heat exchanger is shown in FIG. 1. The pipe 10 generally has a plurality of longitudinally extending inner fins 12 projecting into the pipe and a plurality of longitudinally extending outer fins 13 extending outwards from the pipe. Longitudinally extending fins are often used because they are generally more straightforward to manufacture on cylindrical pipes.
As is well known in the art, the fins provide extended surfaces for augmenting heat transfer between a fluid within the pipe and a fluid flowing outside the pipe. These fins generally belong to a class of devices called xe2x80x9cextended surfacesxe2x80x9d, as they expose more surface area of the pipe, thereby enhancing convective heat transfer. However, it is difficult to efficiently produce a large number of fins on the inner side of the pipe or tube dividing the two fluid flows. Consequently, the performance of small cylindrical heat exchangers suffers as a result of the reduced fin density. It has additionally proved difficult to create extended surfaces on the inner side of a cylindrical heat exchanger pipe that that are not longitudinally extending fins, and particularly to produce staggered pins. Fins have been fabricated in many ways, such as welding, casting, extruding, embedding, wrapped on, or machined from thick stock. However, none of these current methods easily permit the creation of pins or pedestal type fins, particularly staggered ones, on the inner surface of a cylindrical heat exchanger pipe. Both of these factors, namely a high density of fins and fins arranged in a staggered layout, are known to improve the heat transfer performance of a heat exchanger, but have to date been difficult to achieve within cylindrical heat exchanger pipes.
It is an object of the present invention to provide a improved heat exchanger.
It is another object of the present invention to provide a heat exchanger for a gas turbine engine that provides reduced cost, weight, and number of parts.
It is another object of the present invention to provide a cylindrical heat exchanger having improved performance.
It is a further object of the present invention to provide a cylindrical heat exchanger having staggered fins on an inner surface of a conduit thereof.
Therefore, in accordance with the present invention, there is provided a heat exchanger permitting heat transfer between a first and a second fluid conveyed therethrough, comprising: an inner conduit and an outer conduit, the inner conduit defining a first passage for conveying the first fluid therethrough, the inner conduit being inside the outer conduit, and the inner conduit and the outer conduit defining a second passage therebetween for conveying the second fluid therethrough; and at least the inner conduit having a plurality of slots in at least an inner surface thereof, the plurality of slots being provided at least partially in a crisscrossing arrangement, thereby defining a plurality of heat transfer fins on at least the inner surface of the inner conduit.
There is also provided, in accordance with the present invention, a method for forming a plurality of heat transfer fins on at least an inner surface of a conduit in a heat exchanger, the method comprising: forming a plurality of criss-crossing slots in at least a portion of the inner surface of the conduit, the plurality of slots defining the plurality of heat transfer fins therebetween.
There is further provided, in accordance with the present invention, a heat exchanger permitting heat transfer between a first and a second fluid conveyed therethrough, comprising: a first conduit and a second conduit, the first conduit being adapted for conveying the first fluid therein and the second conduit being adapted for conveying the second fluid therein; the first conduit and the second conduit being relatively arranged such that heat transfer between the first fluid and second fluid is permitted; and at least one of the first conduit and the second conduit having a plurality of slots in an inner surface thereof, the plurality of slots being disposed in a criss-crossing arrangement such that a plurality of heat transfer enhancing fins are provided therebetween.